The charity fundraising web page set up by Claire Squires, who collapsed and died while running the London marathon last weekend, has raised more than £1m in less than a week – with tens of thousands of people logging on from all over the world to leave donations.

Squires, 30, a hairdresser, had raised £500 for her chosen charity, The Samaritans, when she began the marathon. But as news of her death spread around the world that figure swelled rapidly.

"This was an emotional tribute to Claire and her spirit, an emotional response," said Rachel Kirby-Rider, executive director of fundraising at Samaritans.

"There's a lot of hardship around in society and seeing the generosity of her spirit, the fact that she was an ordinary girl, and had given up so much of her time and energy for charity, that struck a chord," she added.

At peak times during the past few days, donations to Squires's Just Giving page were flooding in at a rate of £30,000 an hour, with people giving an average of £11. On Friday, the amount raised on Squires's page passed the fundraising website's previous highest total, the £977,000 raised for Help for Heroes by the disabled Iraq war veteran Phil Packer .

The hundreds of short messages left by donors on the page gave an indication of the sense of collective grief and sympathy engendered by Squires's death. She was hailed as "an icon" and an "inspiration". Friends described her as vivacious, upbeat and larger than life.

Speaking to a local newspaper, Claire's father Paul Squires said: "It seems as though my daughter has captured the hearts of a nation. She was a wonderful, loving, giving person and it is some comfort to us as a family that people have responded in this way. It is amazing."

Squires was the 11th participant to die since the event began 31 years ago. She collapsed in Birdcage Walk, near St James's Park, on the final stretch of the 26.2-mile course, just one bend away from the finishing line.

A funeral service will take place on Wednesday at St Andrew's Church in the Leicestershire village of North Kilworth, where her family has a plot. Claire will be buried next to her older brother Grant, who died 11 years ago, at the age of 25.

Just Giving managing director Anne-Marie Huby described the public's response as a spontaneous, "true gesture of sympathy" by thousands of ordinary people. The huge volume of low-sum donations to the site suggested that the public, while hard-pressed financially, were giving as much as they could manage, she added.

Fundraising experts say Squires's story was always likely to unlock donor sympathy. Unpublished research by the Charities Aid Foundation shows that the single most important trigger for donors is feeling emotionally moved by someone's story. The second most important is the tribute effect – the urge to give in memory of somebody.

What was unprecedented was the way social media and digital technology helped drive donations. Squires's death happened at a public, emotionally charged event widely covered by mainstream press and TV. But Twitter and Facebook turned it into a shared story, while the simplicity and directness of online giving enabled people to give quickly and easily.

"What's remarkable is how the page was fuelled by social media, more than we have ever seen before," said Huby.

People who use the site were increasingly using Twitter and Facebook to tell their friends and followers about what they were doing for charity.

"What we saw with Claire Squires was this phenomenon amplified on a global scale," Huby added. Squires's achievement is a ray of light for charities, whose incomes have been battered in an increasingly tough funding environment over the past two years.

While the numbers who give are holding up, people are giving slightly less and to fewer charities, as household incomes become squeezed.

Charities hope social media will encourage more spontaneous giving, particularly among younger people, who are regarded as unreceptive to traditional methods such as direct debit donations and street "chuggers".

A Samaritans spokesman said the mood at the charity's HQ this week was subdued: "We'd give all the money back tomorrow to have Claire be able to finish the marathon and be with her family and partner."

The charity has strong links with the Squires – Claire's mother Cilla has been a volunteer for more than 24 years. It said it will sit down with the family in the next few weeks to discuss how the money – which has been placed in a special memorial fund – will be spent.

"This will be her legacy, and it will be spent on Samaritans projects that she would have been really passionate about," said Kirby-Rider. "It will be about making a real impact: saving more lives."